Isolation and screening of α-amylase and glucoamylase producing fungi and their application in bioethanol production

Abstract

Isolation of α-amylase and glucoamylase producing fungal strains was investigated. Samples (120 in number) were collected aseptically from rice mill industrial areas, cassava processing grounds, potato farms, corn processing industries and refuse dumping sites within Abakaliki metropolis in Ebonyi State of Nigeria. The samples were first grown on solid agar (PDA) and sub-cultured to get their pure cultures. The pure cultures were then grown for 3 days on PDA and screened for starch hydrolysis using Iodine-potassium iodide method. Out of the 120 cultures, 26 showed some degrees of starch hydrolysis. The 26 positive fungal isolates were further screened for enzymatic activities which were measured quantitatively with spectrophotometric methods. However, only 3 isolates (2a, 3 and 6b) were finally selected based on their high α-amylase and glucoamylase activities. Alpha-amylase production by co-cultivation of the selected isolates showed higher activities than single cultures. For instance, the co-culture of isolate 2a and 3 was higher (40.32+0.489 U/ml) than individual activities of isolate 2a (30.55+0.710 U/ml) or isolate 3 (32.44+0.442 U/ml). Bioethanol production was achieved by Simultaneous Saccharification and Fermentation (SSF) process using the selected fungal isolates and Saccharomyces cerevisiae. The bioethanol concentrations were measured quantitatively with boiling/iodometric method. Isolate 3 with the yeast gave the highest concentration of the ethanol (10.913+0.874 g/L) after 96hours followed by isolate 2a and yeast (9.817+0.400 g/L) and then isolate 6b and yeast (8.540+0.308 g/L). Finally, the selected fungal isolates were identified as Aspergillus species (isolate 3), while isolates 2a and 6b were Mucor and Rhizopus species respectively